The design of an efficient charging management system for on-the-move electric vehicles (EVs) has become an emerging research problem in future connected vehicle applications, given their mobility uncertainties. Major technical challenges here involve decision-making intelligence for the selection of charging stations (CSs) and the corresponding communication infrastructure for necessary information dissemination between the power grid and mobile EVs. In this paper, we propose a holistic solution that aims to create a high impact on the improvement of end users' driving experiences (e.g., to minimize EVs' charging waiting time during their journeys) and charging efficiency at the power grid side. In particular, the CS selection decision on where to charge is made by individual EVs for privacy and scalability benefits. The communication framework is based on a mobile publish/subscribe (P/S) paradigm to efficiently disseminate CS condition information to EVs that are on the move. To circumvent the rigidity of having stationary roadside units (RSUs) for information dissemination, we promote the concept of mobility as a service (MaaS) by exploiting the mobility of public transportation vehicles (e.g., buses) to bridge the information flow to EVs, given their opportunistic encounters. We analyze various factors affecting the possibility for EVs to access CS information via opportunistic vehicle-to-vehicle (V2V) communications, and we demonstrate the advantage of introducing buses as mobile intermediaries for information dissemination, based on a common EV charging management system under the Helsinki city scenario. We further study the feasibility and benefit of enabling EVs to send their charging reservations involved for CS selection logic, via opportunistically encountered buses, as well. Results show that this advanced management system improves both performances at the CS and EV sides.